Functional activation of the infant cortex during object processing

Abstract

A great deal is known about the functional organization of the neural structures that mediate visual object processing in the adult observer. These findings have contributed significantly to our conceptual models of object recognition and identification and provided unique insight into the nature of object representations extracted from visual input. In contrast, little is known about the neural basis of object processing in the infant. The current research used near-infrared spectroscopy (NIRS) as a neuroimaging tool to investigate functional activation of the infant cortex during an object processing task that has been used extensively with infants. The neuroimaging data revealed that the infant cortex is functionally specialized for object processing (i.e., individuation-by-feature) early in the first year but that patterns of activation also change between 3 and 12 months. These changes may reflect functional reorganization of the immature cortex or age-related differences in the cognitive processes engaged during the task.

Figure 1

Test events for Experiments 1 and 2. Each cycle of the test event was 10 s and infants saw 2 complete cycles during each test trial. Infants saw the following objects to the left and right sides of the screen, respectively: green ball-green box (shape difference); green ball-red ball (color difference); and green ball-green ball (control).

Figure 2

Configuration and placement of optodes. (a) Location of emitters (large red circles) and detectors (black squares) on the infant’s head in relation to the 10–20 International EEG system (small black circles). Note that an emitter was placed directly over O1, T5, and T3 and one emitter lay near P3. Also represented are the nine corresponding channels from which data were collected. Each detector read from a single emitter except for the detector between T3 and T5, which read from both emitters. The light was frequency modulated to prevent “cross-talk”. (b) Configuration of the emitters (red circles) and detectors (black squares), and the nine channels, in the headgear. Emitter-detector distances were all 2 cm. (c) Infants sat in a supportive seat to restrain excess movement. An elasticized headband was slid onto the infant’s head and secured by a chinstrap.

Figure 3

Neuroimaging data. (a) Relative skull location of each of the nine channels (blue numbers) in relation to the four 10–20 coordinates (red letters/numbers) are overlaid on a representative MRI of a 6-month-old infant. (b) Relative changes in HbO and HbR (red and blue lines respectively) during each test event at each of the nine channels are displayed for Experiment 1 and Experiment 2 separately. Time is on the x-axis and hemodynamic changes in μM cm on the y-axis. The bold lines separate channels associated with each of the four 10–20 coordinates. In both experiments, 1 to 20 s was the test event and 21 to 30 s was the silent pause (baseline). The hemodynamic response was averaged over 6 to 20 s, indicated by grey shading. Asterisks indicate M (SD) responses that differed significantly from baseline (* p < .05, ** p < .01, and *** p < .001 two-tailed).

Figure 4

Patterns of neural activation obtained for the 3- to 5-month-olds and 11- to 12-month-olds in the present experiments and for the 5- to 7-month-olds of Wilcox et al. (2010). The colored dots (large green = shape difference, medium blue = color difference, small yellow = control) indicate that neural activation was obtained during that test event at that channel. The distance between sources and detectors remained fixed but mean head size varied by age (see text). The black lines indicate the actual location of T3, T5, and P3 (based on mean head measurements) for the younger and older infants.